Weeds cost farmers billions of dollars annually in crop losses and in the expense of keeping weeds under control. Much of the cost of intertillage of row crops, maintenance of fallow, seedbed preparation, and seed cleaning is chargeable to weed control. Suppression of weeds along highways and railroad right-of-ways, and in irrigation ditches, navigation channels, yards, parks, grounds, and home gardens also is expensive. Ragweed pollen is the source of annual periodic distress to several million hayfever sufferers. Poison ivy, poison oak, poison sumac, nettles, thistles, sandburs, and puncturevine also bring pain to millions. Weeds also serve as hosts for other crop diseases as well as for insect pests.
The losses caused by weeds in agricultural production environments include decrease in crop yield, reduced crop quality, increased irrigation costs, increased harvesting costs, decreased land value, injury to livestock, and crop damage from insects and diseases harbored by the weeds.
Chemical herbicides have provided an effective method of weed control; however, the public has become concerned about the amount of residual chemicals which might be found in food, ground water, and the environment. Stringent new restrictions on the use of herbicides and the elimination of some effective herbicides from the market place could limit economical and effective options for controlling costly weeds. Additionally, the visually apparent phytotoxic effects of some systemic herbicides appear very slowly on the target weeds, so pesticide users often seek methods by which the apparent speed of action of the herbicide is increased.
Recently, salts of fatty acids, primarily sodium or potassium fatty acid salts, have been used commercially as pesticides. Compositions having excellent pesticidal properties which exploit these salts are available commercially from Safer, Inc., under the trademark SAFER INSECTICIDAL SOAP. A herbicidally active composition utilizing partially saponified fatty acids as the active ingredient is sold by Safer, Inc. under the trademark SHARPSHOOTER. These fatty acid compositions are effective, naturally occuring pesticides which have no known long term environmental effects. Although fatty acid salts have herbicidal activity, it would be desirable to provide an alternative composition having an unsaponified active ingredient while maintaining the environmental compatibility of the pesticide and reducing the eye and skin irritancy of the product.
U.S. Pat. Nos. 2,626,862; 4,975,110; and 5,035,741 describe certain fatty acid compositions useful as herbicides. These documents mention the use of salts of fatty acids. Specifically, "saponified" fatty acids are discussed. Saponification means "to form the sodium or potassium salt of a fatty acid." It stems from the soap making industry where animal fats (esters of fatty acids and glycerol) are hydrolyzed in sodium or potassium hydroxide to form the sodium or potassium salts of the fatty acids (soaps) and free glycerol. Mixing sodium or potassium hydroxide with a free fatty acid to form the salt is also called saponification. "Complete" saponification means that 100% of the fatty acid is converted to the salt; "partial" saponification means that &lt;100% of the acid is converted to the salt. This means there is a mixture of the free fatty acid and the fatty acid salt. U.S. Pat. No. 4,975,110 indicates that the free fatty acid form is preferable to fatty acid salts for use as a herbicide. These patents also teach that the proper formulation of a fatty acid herbicide requires one or more surfactants.
In the past, fatty acid esters have been used as chemical pinching agents for the inhibition of bud growth of certain plants (Tso, T. C., G. L. Steffens, M. E. Engelhaupt [1965] J. Agr. Food Chem. 13(1):78-81; Sill, L. P., P. V. Nelson [1970] J. Amer. Soc. Hort. Sci. 95(3):270-273). However, no general herbicidal activity has been established and, in fact, the literature on this subject as well as the common knowledge in the field taught that herbicidal activity of fatty acid compositions was reduced when esters were formed. Therefore, efforts heretofore have focused on methods for formulating fatty acid herbicides to reduce the possibility of any ester formation through, for example, chemical reaction of the fatty acid with free hydroxyl groups. For this reason, esters and ethers have commonly been used as surfactants rather than compounds with free hydroxyl groups.